1. Field of the Invention
The present invention is in the field of night vision devices. More particularly, the present invention relates to a night vision device which includes provision for secure audio communication, and may also include provision for identifying friendly personnel (IFF).
2. Related Technology
The present night vision devices include both goggle and monocular types which may attach to a support structure carried by a face mask or by a helmet, as well as comparatively small hand-held "pocket scope" types of night vision devices, and comparatively larger weapon-mounted night vision sights. As thus supported in front of a user's face and eyes in front of at least one eye of the user, the night vision device provides an intensified image of a night-time scene. An objective lens or lens system directs light from the night scene, which is too dim to be viewed with natural vision, onto an image intensifier tube. The image intensifier tube effects an amplification of available light and also, in effect, shifts the frequency of invisible infrared light into the visible spectrum. An eyepiece lens or lens system presents the image for viewing by a user of the device. Thus, the image intensifier tube provides a visible image which replicates the dim or invisible infrared image entering the device via the objective lens. Infrared light is rich in the night-time sky, so that a user of a night vision device can see without artificial illumination. The night vision weapon sights also incorporate an aiming reticle for use in sighting the weapon at a target.
The night vision devices which are supported from the user's head it may be used by the wearer of the helmet or face mask to view a night-time scene while the user's hands remain free. Many of these night vision devices include an infrared LED or laser diode lamp which forwardly projects a cone of invisible infrared light. This light is not visible to the unaided eye, but will provide an image through the night vision device. This invisible infrared light may be used, for example, for covert signaling to other personnel who are also equipped with night vision devices. The infrared light may alternatively be used like a flash light in extremely dark conditions for illumination of a limited area around the user without the aid of visible light. Such use allows the user to move about, to read a street sign or a map, for example, and to perform other activities without the use of visible light.
A conventional night vision device is known as the AN/PVS-7B. This night vision device includes a housing with a single objective lens through which is received low-level light from a night-time or other scene illuminated by light too dim to be viewed with the unaided eyes. The housing of the conventional AN/PVS-7B also included an image intensifier tube which provides an image in phosphor green light replicative of the dim scene viewed through the single objective lens. An image splitter, and a pair of eye pieces allow the user of the device to view the full intensified image with each eye.
The conventional AN/PVS-7B also includes a small infrared lamp, the light from which is not visible with the unaided eye, but which will provide an image through the night vision device. This lamp may be switched on for area illumination, for example, in an area where natural or other low-level lighting is nonexistent or is too dim for the night vision device to provide an image. Such area illumination with infrared light may be required, for example, in a building basement or in a tunnel where natural light can not reach, and where artificial illumination visible with the unaided eyes is not available or is not desirable. This small infrared spot light of the conventional night vision devices, such as the AN/PVS-7B, is also useful for such purposes as map or sign reading in circumstances where visible illumination would be undesirable. Covert signaling with the infrared lamp to others who are also equipped with night vision devices is facilitated by a momentary contact switch for this lamp.
However, the increasing availability and presence of night vision devices increases the risk that such supposedly covert signalling using the relatively broad angle infrared beam of conventional night vision devices will be observed by hostile personnel. Further, recent experience has shown that radio communications are increasingly subject to interception. Even those radio communications which are encoded or scrambled are subject to possible code breaking or de-scrambling. Radio transmissions can also reveal the location of the transmitter to unfriendly personnel. Still further, the rapid pace of action and lethality of modern weapons systems in armed conflicts has highlighted the need to quickly identify friendly personnel so that injuries and fatalities do not result from so called "friendly fire".